Flow cytometry enables investigators to identify, purify and characterize cells from mixed populations, based on a pattern of proteins they express. At Columbia University, like most other institutions, the growing need to carry out studies in primary cells has made flow cytometry an increasingly essential tool for biomedical research. These institutional needs are in large part met by the Columbia University Flow Cytometry Core Facility, which currently operates two analytical cytometers (a FACS Calibur and FACScan) and a heavily modified FACStar Plus cell sorter. The sorter, originally purchased in 1991 through a Shared Instrumentation Grant, despite modifications, has reached the limit of its useful life. Moreover, with the development of the new FACS cell-sorting platform, support for the FACStar Plus platform is becoming more difficult. In this proposal we request funding to replace our FACStar Plus with a Becton-Dickinson (B-D) FACS Aria cell sorter. We propose to equip this sorter in its standard 3-laser configuration, providing it with all the features we require to carry out state-of-the-art accurate high-speed multi-parameter cell sorting. Additional support, for both the purchase and operation of this cell sorter will continue to be provided by Columbia University Cancer Center and user fees. Replacing our aging FACStar Plus with a modem FACS Aria cell sorter will not only enable the research community at Columbia University to remain competitive in several areas of biomedical research, but will also facilitate our ability to retain and recruit faculty, especially in the field of immunology.